Rabbit retinal pigment epithelial cells have been cultured over a period of several passages. Ultrastructurally these cells secrete a fibrillar matrix. Biochemically the RPE synthesize both collagen (Type I and Type IV) and elastin. The synthesis of these two components, as well as the synthesis of trypsin susceptible material appears to be controlled by ascorbic acid. Maximal incorporation of proline into an insoluble matrix is obtained with 10 micrograms/ml of ascorbic acid. Collagenase and elastase susceptible substances, however, are found to be synthesized at a greater rate in the presence of 5 micrograms/ml ascorbate, whereas trypsin susceptible substances are synthesized maximally at 10 micrograms/ml ascorbate. The effect of various growth factors on the proliferation of RPE in vitro and on their synthetic capacity is being investigated.